In various lighting applications it is often desirable to adjust the intensity of light generated by one or more light sources. This is typically accomplished via a user-operated device, commonly referred to as a “dimmer,” that adjusts the power delivered to the light source(s). Many types of conventional dimmers are known that allow a user to adjust the light output of one or more light sources via some type of user interface (e.g., by turning a knob, moving a slider, etc., often mounted on a wall in proximity to an area in which it is desirable to adjust the light level). The user interface of some dimmers also may be equipped with a switching/adjustment mechanism that allows one or more light sources to be switched off and on instantaneously, and also have their light output gradually varied when switched on.
Many lighting systems for general interior or exterior illumination often are powered by an alternating current (“AC”) source, commonly referred to as a “line voltage” (e.g., 120 Volts RMS at 60 Hz, 220 Volts RMS at 50 Hz). An AC dimmer typically receives the AC line voltage as an input, and some conventional dimmers provide an AC signal output having one or more variable parameters that have the effect of adjusting the average voltage of the output signal (and hence the capability of the AC output signal to deliver power) in response to user operation of the dimmer. This dimmer output signal generally is applied, for example, to one or more light sources that are mounted in conventional sockets or fixtures coupled to the dimmer output (such sockets or fixtures sometimes are referred to as being on a “dimmer circuit”).
Conventional AC dimmers may be configured to control power delivered to one or more light sources in a number of different ways. For example, the adjustment of the user interface may cause the dimmer to increase or decrease voltage amplitude of the AC dimmer output signal. In other configurations, the adjustment of the user interface may cause the dimmer to adjust the duty cycle of the AC dimmer output signal (e.g., by “chopping-out” portions of AC voltage cycles). This technique is sometimes referred to as “phase modulation” (based on the adjustable phase angle of the output signal). Perhaps the most commonly used dimmers of this type employ a TRIAC device that is selectively operated to adjust the duty cycle (i.e., modulate the phase angle) of the dimmer output signal by chopping-off rising portions of AC voltage half-cycles (i.e., after zero-crossings and before peaks). Other types of dimmers that adjust duty cycles may employ gate turn-off (GTO) thyristors or insulated-gate bipolar transistors (IGBTs) that are selectively operated to chop-off falling portions of AC voltage half-cycles (i.e., after peaks and before zero-crossings).
FIG. 1 generally illustrates some conventional AC dimmer implementations. In particular, FIG. 1 shows an example of an AC voltage waveform 302 (e.g., representing a standard line voltage) that may provide power to one or more conventional light sources. FIG. 1 also shows a generalized AC dimmer 304 responsive to a user interface 305. In the first implementation discussed above, the dimmer 304 is configured to output the waveform 308, in which the amplitude 307 of the dimmer output signal may be adjusted via the user interface 305. In the second implementation discussed above, the dimmer 304 is configured to output the waveform 309, in which the duty cycle 306 of the waveform 309 may be adjusted via the user interface 305.
Both of the foregoing techniques have the effect of adjusting the average power applied to the light source(s), which in turn adjusts the intensity of light generated by the source(s). Incandescent sources are particularly well-suited for this type of operation, as they produce light when there is current flowing through a filament in either direction; as the RMS voltage of an AC signal applied to the source(s) is adjusted (e.g., either by an adjustment of voltage amplitude or duty cycle), the power delivered to the light source also is changed and the corresponding light output changes. With respect to the duty cycle technique, the filament of an incandescent source has thermal inertia and does not stop emitting light completely during short periods of voltage interruption. Accordingly, the generated light as perceived by the human eye does not appear to flicker when the voltage is “chopped,” but rather appears to gradually change.
Other types of conventional dimmers provide a 0-10 volt analog signal as output, wherein the voltage of the output signal is proportional to the desired dimming level. In operation, such dimmers typically provide for 0% dimming (i.e., light output “full on”) when the dimmer output voltage is 10 volts, and 100% dimming (i.e., light output “off”) when the dimmer output voltage is 0 volts. In one aspect, these dimmers may be configured to provide different linear or non-linear output voltage curves (i.e., relationship between output voltage and dimming ratio).
Still other types of conventional dimmers, such as those that employ a DMX512 control protocol in which packets of data may be transmitted to one or more lighting units via one or more data cables (e.g., a DMX512 cable). DMX512 data is sent using RS-485 voltage levels and “daisy-chain” cabling practices. In a typical DMX512 protocol, data is transmitted serially at 250 kbit/s and is grouped into packets of up to 513 bytes, called “frames”. The first byte is always the “Start code” byte, which tells the connected lighting units which type of data is being sent. For example, for conventional dimmers, a start code of zero is typically used.
Yet other types of conventional dimmers output various types of digital signals corresponding to the desired dimming level. For example, some conventional dimmers may implement either the digital signal interface (DSI) protocol or the digital addressable lighting interface (DALI) protocol. When configured as a DALI controller, a dimmer may address and set the dimming status of each lighting unit in the DALI network. This may be accomplished by individually addressing lighting units in the network or by broadcasting a digital message to multiple lighting units to adjust their lighting properties.
Digital lighting technologies, i.e., illumination based on semiconductor light sources, such as light-emitting diodes (“LEDs”), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g., red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Pat. Nos. 6,016,038 and 6,211,626, incorporated herein by reference. Also, some methods for providing power to devices via an A.C. power source, and for facilitating the use of LED-based lighting sources on A.C. power circuits that provide signals other than standard line voltages are disclosed in U.S. Pat. No. 7,038,399, also incorporated herein by reference.
Thus, there is a need in the art to enable efficient encoding of information relating to one or more parameters of the light generated by, for example, LED-based lighting units(s), on the AC line voltage, thereby providing an encoded power signal for controlling and powering the lighting units(s).